Synthesis Of Silicoaluminophosphate Research Articles

Methanol to olefins conversion over silicoaluminophosphates with AEI structure: Effect of the active site type

Effect of the type of active site on the catalytic properties of microporous crystalline silicoaluminophosphates with AEI structure synthesized at 150, 170, and 190°C has been investigated. The state of the active site was changed by varying the catalyst synthesis conditions. It has been established that during the synthesis of silicoaluminophosphates with the AEI structure from the reaction mixture of the same composition, an increase in the temperature and crystallization time leads to an increase of the silicon content and crystal size growth. The observed changes in the physicochemical properties are accompanied by the change of the silicon state in the structure of silicoaluminophosphates with the predominant formation of silicon “islands” via the SM3 mechanism. According to 29Si NMR data, the formation of active sites of silicoaluminophosphates via the SM2 mechanism in the form of isolated silicon atoms in the structure is also observed for these materials. The presence of such sites, along with the morphological features of the crystals, determines the unusual catalytic properties of silicoaluminophosphate with AEI structure in MTO process, which are a high ethylene yield up to 41 wt % at an ethylene: propylene molar ratio of 1: 6.

Effects of careful designing of SAPO-44 catalysts on the efficient synthesis of furfural

Considering the growing importance of furfural, it is necessary to develop a robust solid acid catalyst for the conversion of xylan (hemicelluloses) into furfural in a one-pot method. In this study, the effects of various components (Si, Al and P) and crystallization time on the preparation of acidic materials and their properties are extensively described. It is seen that with the increase in crystallization time (0, 48, 96, 176h) during the synthesis of silicoaluminophosphate (SAPO-44), materials morphology changes from amorphous to AFI to CHA and the best activity for furfural synthesis (82%) from xylan was observed with SAPO-44 catalyst aged for 176h. Since, acidity in the SAPO-44 is guided by the incorporation of Si in the ALPO framework, study on Si molar concentration (0.8, 1.0, 1.2, 1.4 and 1.6) in SAPO-44 was carried out and it was observed that SAPO-44 having 1.0 mole of Si content is the best catalyst for the xylan/xylose conversion to furfural. Catalyst structure–activity correlation is thoroughly defined with the help of several physico-chemical properties.

Study of preparation methods and their effect on the morphology and texture of SAPO-34 for the methanol to olefin reaction

In our present study, the effects of different parameters on the synthesis of silicoaluminophosphate, SAPO-34, were investigated and the product selectivity and catalytic performance of this catalyst were studied for the reaction of methanol to olefins in a fixed bed reactor. In spite of examining the conventional parameters effective in the hydrothermal preparation of SAPO-34, such as templating agents or mixed templating agents with different ratios, different alumina and silica sources, aging time and hydrothermal reaction in static state, we have investigated the effect of the mixing method and the addition of crystal growth inhibitors on the morphology and particle size of the prepared zeolites. The synthesized catalysts have been characterized with several methods such as Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, BET and X-ray powder diffraction. Under our experimental conditions, the prepared SAPO-34 has shown better selectivity to propylene, minimum paraffinic byproducts and a higher percentage of total olefins compared to a commercial ZSM-5 catalyst.